Suspicion `lies in two areas of brain`

Washington: Suspicion lies in two areas of the brain -- the amygdala which correlates strongly with a baseline distrustfulness, and parahippocampal gyrus that acts like a cerebral lie detector, scientists have discovered.

"We wondered how individuals assess the credibility of other people in simple social interactions. We found a strong correlation between amygdala and a baseline level of distrust, which may be based on a person`s beliefs about trustworthiness of other people in general, his or her emotional state, and the situation at hand.

"What surprised us, though, is that when other people`s behaviour aroused suspicion, the parahippocampal gyrus lit up, acting like an inborn lie detector," said Read Montague at the Virginia Tech Carilion Research Institute, who led a team that conducted the research.

For their research, the scientists used functional magnetic resonance imaging to study neural basis of suspicion.

Seventysix pairs of players, each with a buyer and a seller, competed in 60 rounds of a simple bargaining game while having their brains scanned. At the beginning of each round, the buyer would learn the value of a hypothetical widget and suggest a price to the seller.

The seller would then set the price. If the seller`s price fell below the widget`s given value, the trade would go through, with the seller receiving the selling price and the buyer receiving any difference between the selling price and the actual value.

If the seller`s price exceeded the value, though, the trade would not execute, and neither party would receive cash.

The researchers found that buyers fell into three strategic categories: 42 per cent were incrementalists, who were relatively honest about the widget`s value; 37 per cent were conservatives, who adopted the strategy of withholding information; and 21 per cent were strategists, who were actively deceptive, mimicking incrementalist behaviour by sending high suggestions during low-value trials.

The sellers had a monetary incentive to read the buyers` strategic profiles correctly, yet they received no feedback about the accuracy of the information they were receiving, so couldn`t confirm any suspicions about patterns of behaviour.

Without feedback, the sellers were forced to decide whether they should trust the buyers based on the pricing suggestions alone. "The more uncertain a seller was about a buyer`s credibility the more active his or her parahippocampal gyrus became," Montague said in a release.